How to set up your wood stove with hot water and radiators

Before we start: lets start with the terminologies, the rules and myths so you can understand how all this works

A wet back – hot water jacket – water booster – these are pretty much all the same thing.

They are traditionally made from stainless steel or copper and hold (on average) 1ltr of water.

They are installed within the firebox and as the fire is going, the water passes through the hot water jacket – which is heated by the fire.

They are all LOW PRESSURE and CAN NOT be connected to mains pressure hot water systems.

The average hot water jacket will heat up to 2.5 to 5kW of water

Wood Heaters MUST be tested and approved for a hot water jacket to be installed: you can not install these into any heater.

A Wood boiler

These are larger size hot water jackets and heat a lot more water.

These are made from steel and require inhibitor to prevent rusting.

These vary in size and are purpose made to suit the boiler

These vary in size form 8kW to 80kW

You can get different styles of wood boilers from

Wood Stoves with Boilers (also know as High Output Cookers)

Freestanding Wood Boilers

Inbuilt Wood Boilers

Gasification Wood Boilers

Pellet Boilers

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Myths

Myth - You can’t heat your water with a wood heater or wood stove

Fact – Yes you can … Pretty much all wood cookers ( or wood stoves ) are available with a wet back option to heat water

Wood heaters MUST be tested and approved to have a Hot Water jacket installed

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Myth - I can retro fit this to my existing wood heater

Fact - Only if the wood heater is tested and approved to have a hot water jacket fitted

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Myth – The hot water systems give you bad hot water pressure

Fact – Actually this is wrong: there are different types of hot water systems on the market, some give you gravity feed (low pressure) some have heat exchanges that give you mains pressure (or pump pressure) hot water to your home

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Myth – You can't use solar with a wood stove

Fact – Again, this is incorrect, you can: there are different types of hot water services available that have Solar for heating your hot water when the sun is out

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Myth – The bigger the hot water jacket – the better the hot water

Fact – No: if your hot water jacket is over sized and you don't use the water - all you do is boil the water

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Myth - I can run hot water & radiators off any system...

Fact - Yes and no...its all about heating the right amount of hot water to heat the amount water you need to do your hot water and radiators

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Myth - Can I use the hot water to heat hydronic (radiator) panels

Fact - Yes

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How does it heat the water?

Its very simple - hot water is lighter than cold water...so when you light your fire, the fire starts to heat the water.

As the water is getting hotter and hotter, it starts to rise, this is called Thermosyphoning

All the hot water jacket does is heat water, it does not store the water.

So as the water is heating, it then rises into a storage tank

The hotter the fire; the more water is heated

The size of the hot water jacket (or Hot Water Boiler) will determine the actual amount of hot water per hour that can be produced.

Different types of Hot Water Tanks

There are many different sytle of hot water tanks available : they all offer different solutions for your home

Low Pressure In Roof Tanks

These are traditionally installed in the roof of your home

They MUST be installed higher than your wood heater or wood stove

Varying in size, the average tank holds between 315 and 400Ltrs

They are made from Copper, which is then insulated then wrapped in a galvanized outer casing

The fill point is a copper header tank – which is traditionally installed on the side of the tank

The complete tank is your domestic hot water : the pressure of your hot water is determined by the height of the tank

For every meter the tank is above the tap, this calculates to be 100Kpa of water pressure

Example: Town water supply to your home is normally 400Kpa

To get the same pressure to your shower, this style of tank will need to be installed 4mtrs above the shower head in your shower.

MP Tanks

These tanks offer a coil of copper, on average 36mts long, inside the tank – this acts as a heat exchange and is heated by the low pressure water

You use the water from the heat exchange as you would your normal water supply that offers you now pressure to the hot water to your taps

The water in the tank is still Low Pressure and is heated by the wood stove or wood heater

Traditionally a 400Ltr Storage tank is used

Tank dimensions are 900mm High x 900mm Round (Approx sizes used)

When full of water - this tank will weigh up to 440Kg

This system relies on Gravity and the tank MUST be installed higher than the stove / boiler

No pumps / valves / strainers can be installed between the flow and return lines from the tank to the stove

One Tank can combine water for Hydronic Radiators / Domestic Hot Water and Solar Heated Water

These tanks are available all plumbed so you can combine:

Hydronic Water

The Hydronic water is the same water heated by the Wood Boiler or Wood Stove that also is used in the radiators

An Inhibitor is used in this water to prevent rust in your system and prolong the life expectancy

A 22.5 or 45Ltr header tank is used to fill this system

Domestic Water

This water is separated through Copper Manifold (or coil) available

Domestic Hot water requires 4kW of heat to heat (1kW heats 100Ltrs) - this will need to be added to your hydronic loading figures

18mtr and 36mtr Manifolds coils available

Solar water

Solar Heated water through Solar Panels

This heated water can also be stored in this tank through an additional Copper Manifold (or coil) in the base of the tank

Flat solar panels or Tube Solar systems can be used

Solar water has no impact on the Hydronic requirements and is a supplement to the Domestic Hot Water heating requirements

Electric Boost

A 3.6 or 4.8 electric element

Electric booster will only assist the domestic water

Centra Coil Tanks

The Centra Coil tank is a versatile tank - suitable for many installation options

The body of the tank is a S/Steel construction: Offering 315Ltrs of domestic hot water at pressure...all heated with a bottom manifold (coil) at low pressure.

The coil of copper in the bottom of the tank has the hot water for your boiler/stove running through it; which then heats the main tank

By setting up the coil on a low pressure system, you can connect the Centra Tank to any make or model wood heater with a wet back - wood stove or wood boiler

The Centra Coil comes complete with

A 3/6kW electric element is standard

Optional solar connections

How this tank works...

There is a coil of copper in the base of the tank - the hot water from your wood stove or hydronic system uses this coil to heat the S/Steel hot water tank, like an element, but it's a hot water coil rather than an electric element.

There is an additional electric element in the tank that you can set up on Off Peak, for times your wood stove is not operating

Up until now, Vacuum Solar was never really suited to connecting to a Wet Back (Low Pressure Hot Water System) from your Wood Stove or Wood Heater

The Ultimate Solar Vacumm System has been purpose built to connect to a Low Pressure Hot Water system - for any make or model wood heater or wood stove

It offers

Built in header tank

Available for Pitched roof or Flat Roof Installations

Built in Copper Heat Exchange offering "Mains" Pressure hot water supply on a low pressure system

Optional Electric Back up element

With two models to choose from

200Ltr Tank with 24 Tube System

250Lr Tank with 30 Tube System

Typical Plumbing

There are a number of ways to plumb these systems

The basic rules are:

The Hot Water tank MUST be installed above the Wood Stove /Boiler

The flow and return pipes MUST be on a fall (this is known as Gravity Plumbing)

The Flow and return pipe MUST NOT have any valves of any kind installed

The Thermostat is installed on the Flow line as close as possible to the Stove / Boiler

The Pump is traditionally installed on the Return Line.

The system is designed to work in this way

Gravity systems is also known as Thermosyphon systems. It's based that hot water is lighter than cold water - so as soon as there is a temperature increase: the hot water will naturally rise.

As soon as the boiler or stove is slight, 100% of the water will naturally rise into the storage tank - this natural circulation will happen because hot water is lighter than cold water.

Once the water temperature reaches 70°C - 75°C, the thermostat (which is on the hot flow line) will then turn the pump on (which is on the return line) and start to pump the water into the radiators.

Depending on the set up (how many radiators you have) the pump does not use all the hot water...it will only pump 40% - 60% of the water to the radiators, the balance is continuing to go to the hot water storage for your domestic use

How the Domestic Coil Works

Water in storage tanks naturally laminates - the hot water is always hotter in the top 1/3rd of the tank

The "MP" coil is submerged in the hottest part of this water and the heat from the storage (or hydronic water) is transferred through the copper pipe to the domestic water.

Different length coils are used (18 or 36Mr) which will determine how much domestic water you have on demand.

Adding Solar

By Adding Solar Hot Water to the system; you have created an "Off the grid System"

Different brands and your location will determine the solar impact on this system

The Solar WILL NOT assist the Hydronic part of the system: it will only assist with the domestic requirements